The present invention relates to a silicone composition that cures to form a release coating (hereinafter abbreviated as a silicone release coating composition). More specifically, the invention relates to a silicone release composition that gives a cured release coating which exhibits optimal release values against tacky substances and which does not impair the residual adhesion of tacky substances.
Cured films with excellent release properties for tacky substances can be formed on the surface of a substrate, for example, on paper, cardboard, laminated paper, synthetic plastic films, fabrics, synthetic fibers, and metal foils by coating thee substrate with an organopolysiloxane-based silicone release composition and then curing the coated composition.
A general problem associated with dimethylpolysiloxane-based silicone release compositions has been the extremely low peel strength values exhibited by their cured coatings. As a result, it has been necessary to add controlled-release additives (CRAs) to these compositions in order to adjust the peel strength of their cured release coatings. These CRAs are exemplified by the MQ silicone copolymer taught in Japanese Patent Application Laid Open No. 49-27033 [27,033/74] and Japanese Patent Application Laid Open No. 59-84953 [84,953/84] which consists of the R.sub.3 SiO.sub.1/2 and the SiO.sub.4/2 unit wherein R denotes monovalent hydrocarbon groups having no more than 2 carbons. Another example of a CRA is the MQ silicone copolymer taught in Japanese Patent Application Laid Open No. 53-29678 [29,678/78] which consists of the R.sub.3 SiO.sub.1/2, (CH.sub.2 .dbd.CH)R.sub.2 SiO.sub.1/2, and SiO.sub.4/2 units where R again denotes monovalent hydrocarbon groups having no more than 2 carbons.
The addition of these MQ silicone copolymer CRAs to silicone release compositions does serve to increase the peel strength of cured release coatings whose peel strengths are at or below 20 gf/5 cm, for example, in applications with seals, labels, and pressure-sensitive adhesive tape. However, the addition of this particular type of CRA also results in substantial migration of the silicon component into the tacky substance, which significantly impairs the residual adhesion of the tacky substance. Moreover, since these MQ silicone copolymers are solids at room temperature, their addition to silicone release coating compositions results in an increase in composition viscosity, which degrades the coating properties of the composition.